There is no default user for admin console in JBoss AS 7.1. Please go to the <JBOSS_HOME>/bin and run the add-user.sh from terminal and follow the steps as tool guides. That would create the user and you don't need to restart server as it automatically updates the server.

Please copy the host.xml from <JBOSS_HOME>/domain/conf/host.xml to <JBOSS_HOME>/standalone/configuration/ and uncomment the mgmt-users.properties in the same folder to enable admin=admin. It should work.